Field of the Invention
The present invention relates to a device for locking tools in a press brake, and in particular to a press for bending sheet metal or the like.
Description of the Related Art
In the machine tool sector, press brakes configured to give certain bending angles to metal sheets, plates or the like, through cold deformation, are well know.
Press brakes generally consist of a bottom bed defining a fixed surface on which to place the metal sheet and carrying a bending die according to the profile of which said metal sheet is bent.
An upper beam is supported so that it can move towards and away from the bed, along a substantially vertical plane. The beam carries integral therewith a bending tool adapted to cooperate with the die to give the sheet the desired shape.
Movement of the upper beam is generated by hydraulic, mechanical or electrical actuator means, which provide the necessary force for the deformation operation.
The tool generally has a lower end structured to cooperate with the upper surface of the die and an upper portion defining a shank for attaching to the upper beam.
As a function of the type of machining to be carried out, said tool can be single, i.e. with a monolithic body that extends for the whole, or for a part, of the length of the crossbeam, or divided into parts, i.e. consisting of several parts placed side by side in the direction of extension of the crossbeam.
For this purpose, the upper beam can be provided with one or more locking devices (known in the field as “intermediate devices”) that, clamping the shanks of the tools, make them integral therewith to enable pressing.
Among the various shapes and types of shank, some of the more widely used have become standardized shapes to enable tools to be installed on presses of different manufacturers.
According to a very widely used variant, the shank has on at least one side a seat, with a C-shaped grooved profile, in which a retaining tooth of the locking device engages to prevent the tool from slipping out and falling when the locking device is loosened.
Prior art locking devices are generally structured like a clamp and comprise a fixed jaw integral with the upper beam and a movable jaw moved by a closing device adapted to move the movable jaw towards or away from the fixed jaw to clamp or release the tool.
A common problem that occurs in the use of these devices concerns the tool change operations.
There are essentially two methods for inserting and removing the tools in prior art locking devices, as a function of their configuration: by sliding the tool horizontally (parallel to the upper beam) or from below through a combined movement of translation and rotation.
In the first case, the tool is inserted at the sides of the press and is made to slide along the length of the upper beam to the predetermined operating position. This method has some drawbacks, the greatest of which is given by the difficulty and the long implementation times of the operation, which requires long machine stoppages.
Moreover, if the tool mounted on the machine comprises several elements placed side by side, to remove or replace an intermediate element it is necessary to first remove all those that precede it, with a further increase in the time required for replacement.
For these reasons locking devices in which the tool can be inserted from the bottom upwards are preferable as, besides requiring much less time to install or remove a single tool, they also allow an intermediate tool to be replaced without having to remove or shift those that are close to it already installed.
EP 1 244 528 B1 describes a locking device for locking tools in which the movable jaw is provided with a lower tooth, facing the fixed jaw, which rests on a plurality of springs fixed on a protrusion of the same number of safety hooks, on which it exerts, through said springs, the force required to clamp the tool and cause it to rest against the fixed jaw.
The movable jaw is also provided with an upward facing upper tooth, which defines a cavity for insertion of a corresponding spike, projecting from the back of the safety hooks, which enables said safety hooks to remain suspended during clamping or release of the jaws.
This prior art locking device has some problems. A first drawback concerns the production of the teeth on the jaw and of the corresponding spikes and protrusions on the safety hook. These parts in fact require particularly laborious and costly precision machining.
Another problem of this device consists in the fragility of the safety hooks that, having a thin and elongated shape and being subject to continuous knocks against the shank of the tool during operations for insertion and removal of the insert, through time can become deformed or break.
Another problem of the device described above consists in the use of springs to transmit the clamping force from the lower tooth of the movable jaw to the safety hook. In particular, the flat springs, applied to the extrados of the hook, after a certain number of clamping and release cycles can yield or even break.
EP 1 884 298 B1 describes a locking device comprising a first jaw and a second jaw, movable in relation to each other, and safety hooks interposed between the first and the second jaw, provided with a retaining tooth adapted to be inserted into a cavity provided in the shank of the tool. The second jaw is provided with a seat in which said safety hooks are movably housed, said seat being closed, on the opposite side with respect to said first jaw, by an arc-like wall that cooperates, by elastic deformation, with a portion of the safety hook during clamping and release of the second jaw. The seat of the second jaw also houses a transverse bar that engages a claw-like portion of the safety hook to support it inside said seat.
This device also has a highly complex construction, due both to the shape of the safety hook and to the large number of parts to be assembled. Moreover, with this device the clamping force is transferred to the tool through an elastic element that may be prone to breaking after a large number of clamping and release cycles of the device. Moreover, this elastic element must be designed and calibrated to operate correctly both with small and light tools and with very heavy tools.
WO 2011/141774 describes a device for locking tools provided with a movable jaw on which there is obtained a tooth adapted to engage the shank of the tool to maintain it suspended and prevent it from falling when jaw is open.
Said tooth, guided along a clamping path of the jaw, also enables the tool to be taken to rest against the fixed jaw to maintain it in position during bending.
A common characteristic of the aforesaid devices, and of many other prior art devices, is the combination of movements to be imparted on the tool to be able to remove it from the locking device.
More in detail, in prior art devices, disengagement of the shank from the retaining tooth takes place following a rotation of the tool, at times aided by an upward translation. In general, rotation is imparted by pushing the tool in the lower part, located in front of the movable jaw, or otherwise by pulling it toward you.
During rotation the tool is gripped by the operator who, to terminate extraction, subsequently draws it downwards to release the shank completely.
Typically, rotation of the tool alone does not cause immediate disengagement of the shank; however, an accidental knock against the tool, for example during the machine set-up operations, in many cases may suffice for the grooved profile to pass beyond the retaining tooth, causing the tool to fall.
Considering the weight of some tools, which can exceed 25 kg, these episodes are dangerous for the operator in charge of the machine and for any other person in the vicinity thereof.